oop to fp - reader monad

DI_reader.sc

import cats.syntax.option._

// domain layer -----------------------------------------------------------
import monix.eval.Task
import cats.data.ReaderT

case class Movie(id: Int, title: String)

trait MovieRepo {
  def getMovie(id: Int): Task[Option[Movie]]
}
trait UsesMovieRepo {
  val movieRepo: MovieRepo
}

// application layer ----------------------------------------------
val db = Map[Int, Movie](42 -> Movie(42, "A Movie"))
object MovieRepoImpl extends MovieRepo {
  def getMovie(id: Int): Task[Option[Movie]] = Task(db.get(id))
}

trait MovieServiceEnv extends UsesMovieRepo

object MovieServiceEnv extends MovieServiceEnv {
  val movieRepo = MovieRepoImpl
}
object MovieService {
  def getMovie(id: Int): ReaderT[Task, MovieServiceEnv, Option[Movie]] =
    ReaderT(_.movieRepo.getMovie(id))
}
val task1 = MovieService.getMovie(42).run(MovieServiceEnv)

// runtime layer -------------------------------------------------
import scala.concurrent.Await
import monix.execution.Scheduler.Implicits.global
import scala.concurrent.duration._

Await.result(task1.runToFuture, 1.second)

// test environment -------------------------------------------------------
object TestEnvironment extends MovieServiceEnv {
  val movieRepo = new MovieRepo {
    def getMovie(id: Int): Task[Option[Movie]] = Task(Movie(-1, "Test").some)
  }
}
val task2 = MovieService.getMovie(42).run(TestEnvironment)
Await.result(task2.runToFuture, 1.second)